Origin of efficient thermoelectric performance in half-Heusler FeNb$_{0.8}$Ti$_{0.2}$Sb

TL;DR

This study reveals that the excellent thermoelectric performance of FeNb$_{0.8}$Ti$_{0.2}$Sb is due to its stable carrier concentration, dominant electronic thermal conductivity, and electron scattering effects, as evidenced by low-temperature measurements.

Contribution

The paper uncovers the physical origins of high thermoelectric efficiency in FeNb$_{0.8}$Ti$_{0.2}$Sb through comprehensive low-temperature transport measurements.

Findings

Nearly temperature-independent optimal carrier concentration

Electronic thermal conductivity dominates above 200 K

Single hole carrier enhances Seebeck coefficient

Abstract

A half-Heusler material FeNb$_{0.8}$Ti$_{0.2}$Sb has been identified as a promising thermoelectric material due to its excellent thermoelectric performance at high temperatures. The origins of the efficient thermoelectric performance are investigated through a series of low-temperature (2 - 400 K) measurements. The high data coherence of the low and high temperatures is observed. An optimal and nearly temperature-independent carrier concentration is identified, which is ideal for the power factor. The obtained single type of hole carrier is also beneficial to the large Seebeck coefficient. The electronic thermal conductivity is found to be comparable to the lattice thermal conductivity and becomes the dominant component above 200 K. These findings again indicate that electron scattering plays a key role in the electrical and thermal transport properties. The dimensionless figure of merit is thus mainly governed by the electronic properties. These effects obtained at low temperatures with the avoidance of possible thermal fluctuations together offer the physical origin for the excellent thermoelectric performance in this material.